Sepsis, Pressure Ulcer, and MRSA Colonization: Principal Diagnosis and Query Decision
Mr. R, a 76-year-old male, is admitted from a skilled nursing facility with fever of 39.1°C, hypotension (82/50 mmHg), confusion, and lactic acidosis (4.2 mmol/L). Blood and urine cultures grow Klebsiella pneumoniae. The provider documents “severe sepsis secondary to Klebsiella urinary tract infection” and “acute kidney injury.” The patient also has a stage 4 sacral pressure ulcer with eschar; wound culture grows MRSA, but the provider writes “MRSA colonization, no wound infection.” Comorbidities include type 2 diabetes with stage 3b chronic kidney disease. IV antibiotics and fluids are started, and the patient is transferred to the ICU. The coder must assign the principal diagnosis and determine whether the pressure ulcer or MRSA result changes sequencing. A second coder suggests coding the pressure ulcer as principal because it is a chronic problem that may have seeded the infection.
1. What is the principal diagnosis, and how should the codes be sequenced? Support your answer with coding guidelines.
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The principal diagnosis is sepsis due to Klebsiella (A41.59), not the pressure ulcer. Under the ICD-10-CM Official Guidelines, when sepsis is present on admission and is the reason for admission, sepsis is sequenced first, followed by the localized infection and the organism code. The pressure ulcer is a secondary diagnosis unless the provider specifically documents that the admission was for ulcer treatment and sepsis was not present on admission-which is not the case here.
A defensible sequence is:
- A41.59 - Sepsis due to other Gram-negative organisms (Klebsiella)
- N39.0 - Urinary tract infection, site not specified
- B96.1 - Klebsiella pneumoniae as the cause of diseases classified elsewhere
- N17.9 - Acute kidney injury, unspecified
- L89.154 - Stage 4 pressure ulcer of sacral region
- E11.22 - Type 2 diabetes mellitus with diabetic chronic kidney disease
- N18.32 - Chronic kidney disease, stage 3b
The MRSA wound culture alone does not justify coding a MRSA infection because the provider documented colonization, not infection. Colonization is not coded. If the provider later documents “MRSA wound infection,” a query should clarify the clinical significance and the appropriate infection code.
2. The second coder wants to make the pressure ulcer the principal diagnosis. What query, if any, is needed, and what documentation would change the answer?
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No query is needed to overturn the sepsis sequence based on the current record. The admission was driven by fever, hypotension, lactic acidosis, and positive blood cultures; the provider explicitly linked sepsis to the urinary tract infection. The pressure ulcer is a chronic comorbidity and is coded secondarily.
A query is appropriate only for genuine ambiguity: the MRSA result and whether the pressure ulcer is infected or the source of sepsis. A compliant query would ask: “The wound culture grew MRSA and the provider documented colonization. Please clarify whether the patient has a MRSA wound infection or colonization only.” If the provider answers “infection,” the coder may add the appropriate infection code but sepsis still remains principal because it was present on admission and chiefly responsible for the admission. The pressure ulcer would become principal only if the record showed the patient was admitted specifically for ulcer care, sepsis developed after admission, and the provider documented that sequence-none of which is present.
3. How does incorrect principal diagnosis assignment affect MS-DRG payment and audit risk?
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The principal diagnosis determines the Medicare-Severity DRG (MS-DRG) and the major diagnostic category. Sepsis as principal with a major complication or comorbidity (MCC) generally groups to a high-weight sepsis DRG. Assigning a pressure ulcer as principal would move the case into a different MDC and DRG, potentially changing payment and reported quality measures. That shift also affects the hospital’s case-mix index and publicly reported data.
Audit risk is significant because the record contains positive blood cultures, hypotension, and provider documentation linking sepsis to the UTI. A reviewer would expect sepsis first. If the coder selected the ulcer to increase payment, the claim could be treated as an overpayment and potentially a false claim. The safer practice is to code from the provider’s diagnostic statement, use a compliant query only for ambiguity, and retain the query and rationale in the record.